I finished doing so redstone and I quitted the world. When I came back, thsi happened. (Look at Photo)
This was shown in the Game Output:
[15:46:23] [Server thread/INFO]: Saving chunks for level '§6After §4The §6Sun §4Sets'/Overworld
[15:46:23] [Server thread/INFO]: Saving chunks for level '§6After §4The §6Sun §4Sets'/Nether
[15:46:23] [Server thread/INFO]: Saving chunks for level '§6After §4The §6Sun §4Sets'/The End
[15:46:40] [Server thread/WARN]: The save is being accessed from another location, aborting
May have different causes:
Antivirus software
Malware
MC-85448
You've opened that world in a second intance of Minecraft
Which of those causes is plausible ?